Hubble Catches Scattered Light From the Boomerang
Nebula

The Hubble Space Telescope has "caught"
the Boomerang Nebula in these
new images taken with the Advanced Camera for Surveys.
This reflecting
cloud of dust and gas has two nearly symmetric lobes
(or cones) of
matter that are being ejected from a central star.
Over the last 1,500
years, nearly one and a half times the mass of our
Sun has been lost
by the central star of the Boomerang Nebula in an
ejection process
known as a bipolar outflow. The nebula's name is
derived from its
symmetric structure as seen from ground-based telescopes.
Hubble's
sharp view is able to resolve patterns and ripples
in the nebula very
close to the central star that are not visible from
the ground.

Astronomers are uncertain of the cause of bipolar
outflow in this, and
many other, young nebulae like the Boomerang. It
may be that a disk of
slow-moving material is situated around the equator
of the star, thereby
blocking more rapidly moving ejected material there,
and allowing only
matter closer to the poles to be ejected. Another
consideration may be
that magnetic fields are responsible for constraining
the material and
thus causing the double-lobed shape of the nebula.

Bipolar outflows are seen to occur both from very
young stars ("protostars") that are still
in the process of collapsing and forming, and from
old stars nearing the ends of their lives that have
become bloated red giants. The Boomerang is believed
to be the ejected outer layers from an old red giant.
Each lobe of the Boomerang Nebula is nearly one
light-year in length, making the total length of
the nebula half as long as the distance from our
Sun to our nearest neighbors- the Alpha Centauri
stellar system, located roughly 4 light-years away.

These images of the Boomerang were taken in early
2005 with the Advanced Camera for Surveys onboard
Hubble. A visible light filter was used in combination
with a series of polarization filters. Similar to
polarizing sunglasses that are used to reduce the
amount of scattered light that enters our eyes on
a sunny day, the telescope's polarizing filters
allow only light of a specific polarization angle
to pass through to the camera's detector. By combining
images taken at different polarization angles, astronomers
can study light scattering in the nebula and the
properties of the small dust particles responsible
for the scattering. The resultant image is a multi-hued
composite of subtle pastel colors.

The Boomerang Nebula is located about 5,000 light-years
from Earth in
the direction of the Southern constellation Centaurus.
Submillimeter
radio measurements made in 1995 show the deep interior
of the nebula
to have a temperature of only one degree Kelvin
above absolute zero,
with absolute zero equal to nearly -460 degrees
Fahrenheit. This
makes the inner regions of the Boomerang Nebula
one of the coldest
known places in the universe.